There was no clear reason why the north ground controller gave Tractor197 authorization to proceed on a route that crossed the active runway without co-ordination with the north tower controller. At the time of the occurrence, he was handling a heavy load of ground traffic, though not complex, mostly taxiing for take-off on Runway15L. The workload was exacerbated by the need to provide amended clearances to many of the aircraft. He went about his duties competently up to the point of the occurrence. His tasks, although quantitatively heavy, were routine and repetitive. His performance was therefore skill-based, essentially responding automatically to routine demands in a highly familiar, but task-saturated, situation. It was an unconscious momentary lapse of attention that led the controller to authorize Tractor197 to proceed with an implicit clearance across the active Runway15L. In skill-based performance, this kind of failure mode is considered to be one of inattention, specifically, a capture error11 wherein the performance of the correct action, that is, the sequence of actions required to clear Tractor197 across an active runway, was interfered with by a stronger habit pattern associated with that runway not being active and, therefore, not requiring co-ordination with the tower controller. The controller may have been under a degree of personal duress due to the hospitalization of his mother. The tower supervisor was aware of the situation, and, although somewhat surprised that the controller had not requested time off, accepted his decision to work on the day of the occurrence. Prior to the incursion, there was nothing in the controller's behaviour or performance to indicate to the tower supervisor or to his co-workers that he was having any difficulty or was otherwise unfit to perform his normal duties. The amendment to the ATC MANOPS requiring that aircraft and vehicles be instructed to either 'cross' or 'holdshort' of any runway it will cross while taxiing or operating on the airport manoeuvring area had become effective five days before the occurrence. The controller was aware of it. Clearances given to other aircraft conformed with the new requirement. The lapse of awareness that led the controller to overlook the fact that the route of Tractor197 crossed a runway, also led him to omit an explicit instruction to cross or hold short. The requirement to provide an explicit clearance may serve as a defence against pilot or vehicle operator inattention, but it is ineffective against a lapse on the part of the controller. Also, it is clear from the Transport Canada report that the requirement for specific ATC clearance across all runways was targeted against pilot inattention, not air traffic controllers. The recommendation in the NAV CANADA report that authorization be required for all aircraft and vehicle movements to cross runways, whether active or not, has the potential to offer an effective defence against controller error or forgetfulness. The pilot/vehicle operator would serve as an independent safeguard against a lapse, such as committed by the controller in this case, by holding short until getting an explicit clearance to cross. Such a level of defence is not assured by implementation measures to date. The present requirement in the AIP addresses only pilots and only when taxiing for departure. There is no corresponding requirement for pilots taxiing to the ramp after arrival, nor is there a national regulatory means to impose the same requirement on vehicle operators. The procedural change adopted by NAV CANADA, requiring that controllers give an explicit clearance to aircraft and vehicles to cross any runway, whether active or inactive, was accompanied by a regulatory change by Transport Canada requiring that pilots hold short of any runway, whether active or inactive, unless they have an explicit clearance to cross. The regulatory change was published in the AIP as part of the 84-day revision that involved numerous routine page replacements without any mention, conspicuous or otherwise, to heighten awareness that one page mandated a new procedure to prevent incursions. Without more conspicuous presentation, such as in the Aviation Safety Newsletter, this change may not have been noticed by some pilots. The procedural change by NAV CANADA was not mentioned at all in the Aerodrome Safety Circular or other material sent to airport operators. In response to the SCRI recommendation for a comprehensive awareness program, Transport Canada, under the auspices of IPAT, has undertaken promotional activities to increase awareness of the problem and to encourage adherence to incursion prevention measures. Issues such as signage and markings have been highlighted, but new measures such as the procedural/regulatory change have not. The Aviation Safety Newsletter and AIP are distributed directly to pilots. The media that are relevant to vehicle operators, such as the Aerodrome Safety Circular, posters and a video, are distributed to airport operators and depend on voluntary initiatives and local programmes in order to reach vehicle operators. They are not necessarily effective in creating awareness amongst airport vehicle operators. Awareness of potential conflicts by vehicle drivers is limited by them being on a different radio frequency than the aircraft being cleared for take-off, with the result that drivers are unaware of the precise status of arriving and departing aircraft. It is normal practice for ground traffic to remain on the ground control frequency rather than changing to the tower frequency for clearance across active runways. The ground controller co-ordinates crossings of active runways with the tower controller; this means that no one outside the control tower, specifically the operators of vehicles or taxiing aircraft, has sufficient situational awareness to offer an effective defence in the event of error in the control tower. When Runways 15L/33R and15R/33L are in use, the overall ATC workload in the tower appears to be reduced because of their lower overall capacity, compared to simultaneous parallel operations from Runways05/23 and06L/24R. While the capacity limitation reduces the quantity of traffic being handled by tower controllers, it has the opposite effect on ground controllers because of the backlog that builds up on the ground. When Runways15L/R are in use, the backlogged ground traffic from all three terminals is concentrated on the north ground controller. The north ground controller also has to handle ground traffic crossing Runway15L, with the added workload of coordinating with tower and closely monitoring the runway.crossing. As a result, the north ground controller experiences an inordinately high workload when Runway15L is active. This situation is not recognized as cause to activate the centre ground controller position or to offload runway-crossing traffic to the tower controller. As commissioned, the RIMCAS provides a stage1 alarm, a visual indication on the ASDE display but no audible signal, when an intruding aircraft or vehicle passes the runway edge in good visibility or 100feet back from the runway edge in poor visibility. A stage2 audible alarm sounds only when the aircraft taking off exceeds a speed of 60knots. Had the RIMCAS, in this configuration, been operating at the time of the occurrence, it probably would not have alerted tower controllers early enough to allow them to warn the flight crew before they detected and reacted to the incursion on their own. That warning may have been insufficient to prevent an accident had the intruder been closer to Flight757 on its take-off run. This occurrence has resulted in some changes at Toronto/LBPIA with regard to vehicle operators, as a result of changes made by the GTAA to procedures that are within their purview. The lack of a national AVOP program inhibits the dissemination of lessons learned to other airports.Analysis There was no clear reason why the north ground controller gave Tractor197 authorization to proceed on a route that crossed the active runway without co-ordination with the north tower controller. At the time of the occurrence, he was handling a heavy load of ground traffic, though not complex, mostly taxiing for take-off on Runway15L. The workload was exacerbated by the need to provide amended clearances to many of the aircraft. He went about his duties competently up to the point of the occurrence. His tasks, although quantitatively heavy, were routine and repetitive. His performance was therefore skill-based, essentially responding automatically to routine demands in a highly familiar, but task-saturated, situation. It was an unconscious momentary lapse of attention that led the controller to authorize Tractor197 to proceed with an implicit clearance across the active Runway15L. In skill-based performance, this kind of failure mode is considered to be one of inattention, specifically, a capture error11 wherein the performance of the correct action, that is, the sequence of actions required to clear Tractor197 across an active runway, was interfered with by a stronger habit pattern associated with that runway not being active and, therefore, not requiring co-ordination with the tower controller. The controller may have been under a degree of personal duress due to the hospitalization of his mother. The tower supervisor was aware of the situation, and, although somewhat surprised that the controller had not requested time off, accepted his decision to work on the day of the occurrence. Prior to the incursion, there was nothing in the controller's behaviour or performance to indicate to the tower supervisor or to his co-workers that he was having any difficulty or was otherwise unfit to perform his normal duties. The amendment to the ATC MANOPS requiring that aircraft and vehicles be instructed to either 'cross' or 'holdshort' of any runway it will cross while taxiing or operating on the airport manoeuvring area had become effective five days before the occurrence. The controller was aware of it. Clearances given to other aircraft conformed with the new requirement. The lapse of awareness that led the controller to overlook the fact that the route of Tractor197 crossed a runway, also led him to omit an explicit instruction to cross or hold short. The requirement to provide an explicit clearance may serve as a defence against pilot or vehicle operator inattention, but it is ineffective against a lapse on the part of the controller. Also, it is clear from the Transport Canada report that the requirement for specific ATC clearance across all runways was targeted against pilot inattention, not air traffic controllers. The recommendation in the NAV CANADA report that authorization be required for all aircraft and vehicle movements to cross runways, whether active or not, has the potential to offer an effective defence against controller error or forgetfulness. The pilot/vehicle operator would serve as an independent safeguard against a lapse, such as committed by the controller in this case, by holding short until getting an explicit clearance to cross. Such a level of defence is not assured by implementation measures to date. The present requirement in the AIP addresses only pilots and only when taxiing for departure. There is no corresponding requirement for pilots taxiing to the ramp after arrival, nor is there a national regulatory means to impose the same requirement on vehicle operators. The procedural change adopted by NAV CANADA, requiring that controllers give an explicit clearance to aircraft and vehicles to cross any runway, whether active or inactive, was accompanied by a regulatory change by Transport Canada requiring that pilots hold short of any runway, whether active or inactive, unless they have an explicit clearance to cross. The regulatory change was published in the AIP as part of the 84-day revision that involved numerous routine page replacements without any mention, conspicuous or otherwise, to heighten awareness that one page mandated a new procedure to prevent incursions. Without more conspicuous presentation, such as in the Aviation Safety Newsletter, this change may not have been noticed by some pilots. The procedural change by NAV CANADA was not mentioned at all in the Aerodrome Safety Circular or other material sent to airport operators. In response to the SCRI recommendation for a comprehensive awareness program, Transport Canada, under the auspices of IPAT, has undertaken promotional activities to increase awareness of the problem and to encourage adherence to incursion prevention measures. Issues such as signage and markings have been highlighted, but new measures such as the procedural/regulatory change have not. The Aviation Safety Newsletter and AIP are distributed directly to pilots. The media that are relevant to vehicle operators, such as the Aerodrome Safety Circular, posters and a video, are distributed to airport operators and depend on voluntary initiatives and local programmes in order to reach vehicle operators. They are not necessarily effective in creating awareness amongst airport vehicle operators. Awareness of potential conflicts by vehicle drivers is limited by them being on a different radio frequency than the aircraft being cleared for take-off, with the result that drivers are unaware of the precise status of arriving and departing aircraft. It is normal practice for ground traffic to remain on the ground control frequency rather than changing to the tower frequency for clearance across active runways. The ground controller co-ordinates crossings of active runways with the tower controller; this means that no one outside the control tower, specifically the operators of vehicles or taxiing aircraft, has sufficient situational awareness to offer an effective defence in the event of error in the control tower. When Runways 15L/33R and15R/33L are in use, the overall ATC workload in the tower appears to be reduced because of their lower overall capacity, compared to simultaneous parallel operations from Runways05/23 and06L/24R. While the capacity limitation reduces the quantity of traffic being handled by tower controllers, it has the opposite effect on ground controllers because of the backlog that builds up on the ground. When Runways15L/R are in use, the backlogged ground traffic from all three terminals is concentrated on the north ground controller. The north ground controller also has to handle ground traffic crossing Runway15L, with the added workload of coordinating with tower and closely monitoring the runway.crossing. As a result, the north ground controller experiences an inordinately high workload when Runway15L is active. This situation is not recognized as cause to activate the centre ground controller position or to offload runway-crossing traffic to the tower controller. As commissioned, the RIMCAS provides a stage1 alarm, a visual indication on the ASDE display but no audible signal, when an intruding aircraft or vehicle passes the runway edge in good visibility or 100feet back from the runway edge in poor visibility. A stage2 audible alarm sounds only when the aircraft taking off exceeds a speed of 60knots. Had the RIMCAS, in this configuration, been operating at the time of the occurrence, it probably would not have alerted tower controllers early enough to allow them to warn the flight crew before they detected and reacted to the incursion on their own. That warning may have been insufficient to prevent an accident had the intruder been closer to Flight757 on its take-off run. This occurrence has resulted in some changes at Toronto/LBPIA with regard to vehicle operators, as a result of changes made by the GTAA to procedures that are within their purview. The lack of a national AVOP program inhibits the dissemination of lessons learned to other airports. The north ground controller inadvertently cleared Tractor197, with an AirbusA310 aircraft in tow, across the active runway at the same time as Flight757 was cleared for take-off by the north tower (on-job trainee) controller. The north ground controller clearance to Tractor197 did not contain an explicit instruction to 'cross' the runway as required by the Air Traffic Control Manual of Operations (ATC MANOPS), nor did the north ground controller co-ordinate the movement of Tractor 197 with the north tower controller. Task saturation of the north ground controller, as a result of weather delays and a runway change, likely contributed to his momentary lapse of attention. Airside vehicle operators are not required to stop and hold short of runways, as are pilots, if they do not have an explicit clearance from ATC to cross that specific runway. As a result, vehicle operators do not serve, as do pilots, as an independent defence against air traffic control error.Findings as to Causes and Contributing Factors The north ground controller inadvertently cleared Tractor197, with an AirbusA310 aircraft in tow, across the active runway at the same time as Flight757 was cleared for take-off by the north tower (on-job trainee) controller. The north ground controller clearance to Tractor197 did not contain an explicit instruction to 'cross' the runway as required by the Air Traffic Control Manual of Operations (ATC MANOPS), nor did the north ground controller co-ordinate the movement of Tractor 197 with the north tower controller. Task saturation of the north ground controller, as a result of weather delays and a runway change, likely contributed to his momentary lapse of attention. Airside vehicle operators are not required to stop and hold short of runways, as are pilots, if they do not have an explicit clearance from ATC to cross that specific runway. As a result, vehicle operators do not serve, as do pilots, as an independent defence against air traffic control error. There is a high volume of traffic between east-side terminals and the infield and central de-icing facility to the west of Runway15L/33R at Toronto/LesterB. Pearson International Airport. This is a hazard with the potential for serious consequences at night or in poor visibility. The north ground controller has an inordinately high workload whenever Runway15L is in operation. A third ground controller position (centre ground) is available for certain high-workload situations, but is not typically used when Runway 15L is in use. Transport Canada's runway incursion prevention program is focused on pilot deviations; NAV CANADA's is focused on controllers. Present efforts to promote awareness of the runway incursion problem do not communicate directly with, and therefore do not necessarily reach, airside vehicle operators.Findings as to Risk There is a high volume of traffic between east-side terminals and the infield and central de-icing facility to the west of Runway15L/33R at Toronto/LesterB. Pearson International Airport. This is a hazard with the potential for serious consequences at night or in poor visibility. The north ground controller has an inordinately high workload whenever Runway15L is in operation. A third ground controller position (centre ground) is available for certain high-workload situations, but is not typically used when Runway 15L is in use. Transport Canada's runway incursion prevention program is focused on pilot deviations; NAV CANADA's is focused on controllers. Present efforts to promote awareness of the runway incursion problem do not communicate directly with, and therefore do not necessarily reach, airside vehicle operators. There is no automated runway incursion warning system, such as inductive loop or similar technology, that warns pilots directly of incursions; the runway incursion monitor/collision avoidance system (RIMCAS) may not provide sufficient warning to prevent an accident. Ground traffic crossing an active runway is not changed to the frequency of the controller controlling that runway and is therefore unable to hear clearances given to aircraft taking off or landing. With the discontinuation of TP2633, Manual of Airport Traffic Directives for the Operation of Vehicles on Airport Movement Areas, there is no national standard that regulates airside vehicle operations. The runway incursion prevention program, influenced by the statistical predominance of pilot deviations in day VFR, does not necessarily address underlying hazards to night and IFR operations. The awareness program including the Aviation Safety Newsletter has not publicized new procedures and regulations recently adopted as preventive measures against runway incursions. As a result, the recent changes concerning clearances across runways may have gone unnoticed. Explicit information is not available as to the status of the recommendations of the Transport Canada subcommittee on runway incursions or of the NAV CANADA runway incursion study.Other Findings There is no automated runway incursion warning system, such as inductive loop or similar technology, that warns pilots directly of incursions; the runway incursion monitor/collision avoidance system (RIMCAS) may not provide sufficient warning to prevent an accident. Ground traffic crossing an active runway is not changed to the frequency of the controller controlling that runway and is therefore unable to hear clearances given to aircraft taking off or landing. With the discontinuation of TP2633, Manual of Airport Traffic Directives for the Operation of Vehicles on Airport Movement Areas, there is no national standard that regulates airside vehicle operations. The runway incursion prevention program, influenced by the statistical predominance of pilot deviations in day VFR, does not necessarily address underlying hazards to night and IFR operations. The awareness program including the Aviation Safety Newsletter has not publicized new procedures and regulations recently adopted as preventive measures against runway incursions. As a result, the recent changes concerning clearances across runways may have gone unnoticed. Explicit information is not available as to the status of the recommendations of the Transport Canada subcommittee on runway incursions or of the NAV CANADA runway incursion study. The TSB held a meeting with the Greater Toronto Airport Authority (GTAA), at which it was suggested that the GTAA may wish to consider having airside vehicle operators get explicit clearances across all runways, consistent with the NAV CANADA instruction to controllers and Aeronautical Information Publication (AIP) section RAC 4.2.5 requirement for pilots. The GTAA responded very quickly by issuing an urgent safety bulletin outlining the requirement and emphatically requiring that the vehicle operator must stop short of the mandatory hold line for a runway, whether active or inactive, if he does not have a specific authorization to proceed12. NAV CANADA has considered activating the centre ground controller position when Runway15L/33R is active. NAV CANADA does not plan to implement a third ground controller on a regular basis. The third ground controller is implemented when staff is available under adverse weather/traffic conditions. This is the procedure that has been in practice during the three years prior to the occurrence. NAV CANADA considered requiring vehicle traffic crossing runways to be on tower frequency rather than ground frequency. A limited trial was conducted, constrained by some vehicles not having tower frequency. It resulted in an unacceptable increase in controller workload, and crossings of non-active runways distracted the controller from the active runway. Transport Canada has recognized the need to update Canadian Aviation Regulation302 and TP312, Aerodrome Standards and Recommended Practices, regarding airside vehicle operations. New draft regulations and standards were presented to the Canadian Aviation Regulation Advisory Committee (CARAC) PartIII Technical Committee in April2002 proposing to strengthen the regulatory requirements with respect to, interalia, procedures for access and control of vehicles. The documents are now at a working group level for final recommendations for improvements.Safety Action The TSB held a meeting with the Greater Toronto Airport Authority (GTAA), at which it was suggested that the GTAA may wish to consider having airside vehicle operators get explicit clearances across all runways, consistent with the NAV CANADA instruction to controllers and Aeronautical Information Publication (AIP) section RAC 4.2.5 requirement for pilots. The GTAA responded very quickly by issuing an urgent safety bulletin outlining the requirement and emphatically requiring that the vehicle operator must stop short of the mandatory hold line for a runway, whether active or inactive, if he does not have a specific authorization to proceed12. NAV CANADA has considered activating the centre ground controller position when Runway15L/33R is active. NAV CANADA does not plan to implement a third ground controller on a regular basis. The third ground controller is implemented when staff is available under adverse weather/traffic conditions. This is the procedure that has been in practice during the three years prior to the occurrence. NAV CANADA considered requiring vehicle traffic crossing runways to be on tower frequency rather than ground frequency. A limited trial was conducted, constrained by some vehicles not having tower frequency. It resulted in an unacceptable increase in controller workload, and crossings of non-active runways distracted the controller from the active runway. Transport Canada has recognized the need to update Canadian Aviation Regulation302 and TP312, Aerodrome Standards and Recommended Practices, regarding airside vehicle operations. New draft regulations and standards were presented to the Canadian Aviation Regulation Advisory Committee (CARAC) PartIII Technical Committee in April2002 proposing to strengthen the regulatory requirements with respect to, interalia, procedures for access and control of vehicles. The documents are now at a working group level for final recommendations for improvements.